1. Field of the Invention
The present invention relates generally to microwave telemetry and, more specifically, to a transponder-based microwave telemetry apparatus for sensing conditions in or on machinery.
2. Description of the Related Art
It is known to sense conditions in machinery such as an internal combustion engine or a torque converter for a motor vehicle. Typically, the engine includes an engine block having a plurality of cylinders and reciprocating pistons disposed in the cylinders. The pistons are reciprocated by a crankshaft via connecting rods.
It is desirable to monitor or sense temperature, pressure, strain, acceleration, proximity, velocity, etc. inside machinery such as the internal combustion engine. However, it becomes difficult to get the sensed conditions off of moving parts and out of enclosed areas of the engine as a reliable, usable signal and in a cost effective manner. For example, it has been proposed to bring signals out of the engine using slip rings and/or mechanical linkages. These have a number of inherent disadvantages. Slip rings are susceptible to electrical noise, which affects reliability. Mechanical linkages are difficult to install, requiring extensive modifications to the engine, and are limited as to the speeds to which they can be exposed, i.e. engine R.P.M.
It is also known to provide a microwave telemetry apparatus for sensing conditions. An example of such an apparatus is disclosed in U.S. Pat. No. 5,555,457 to Campbell et al., the disclosure of which is hereby incorporated by reference. In that patent, an apparatus includes a sensor to sense the interior pressure of a torque converter and generate an electrical signal representative of that pressure. The apparatus also includes a microwave transmitter located within the torque converter, which converts the electrical signal to microwave energy, which is radiated into the interior of the torque converter. The apparatus further includes a stationary receiving microwave antenna exposed to the interior of the torque converter to receive the microwaves and transmit an electrical signal corresponding the microwave energy to a remote receiving device external of the torque converter.
A number of techniques are currently used to measure the temperature of a piston in an internal combustion engine. For example, infrared telemetry transmits information “line-of-sight” as pulses of infrared light from the paths to a stationary photodetector disposed in the crankcase of the engine. Another example is the contact point method, which maintains continuous sliding electrical contact between the piston and the stationary contact on the engine block. Yet another example is the induction coil method that transmits information only at the top or bottom of piston travel when a moving secondary coil on the system is coupled with a stationary primary coil on the engine. Still another example is an “L-Link” or “Grasshopper” linkage, which is designed to support the information carrying wire harness from the piston to outside the engine. A further example is radio frequency telemetry, which transmits information from the piston by way of a radio transmitter mounted on the piston, which transmits waves to an antenna in the crankcase of the engine. Yet a further example is “templugs” which are small threaded plugs made of alloy steel with a special heat treatment. After exposure to elevated temperatures, the plugs will undergo an annealing process and the hardness of the plugs is measured to determine what temperature they were exposed.